Cenvat credit is available on which amount

If excise duty paid by manufacturer or producer of final products less due to price variation clause with comparison to excise duty payable i.e. amount is chargeable in “Original for buyer” in seller invoice. My q is that Cenvat credit available to manufacturer or producer of final products on which amount as per CENVAT CREDIT RULES, 2004 For e.g. manufacturer or producer of final products paid Rs. 99.00 (due to price variation clause) excise duty payable Rs. 100.00 i.e. amount is chargeable in “Original for buyer” in seller invoice.